In recent years, conveyor belts with energy saving specifications which can reduce the power consumption of motors for driving belts have become widespread. In such conveyor belts with energy saving specifications, a low loss rubber, rubber with a small value of a loss factor tanδ which is an energy loss index, is used as a rubber which forms a lower cover rubber layer that comes in contact with support rollers (for example, see Japanese Unexamined Patent Application Publication No. H11-139523A). The loss factor tanδ is a value calculated from E″/E′ using a storage elastic modulus E′ and a loss elastic modulus E″ of the rubber. The smaller the value of the loss factor tanδ, the smaller the amount of energy dissipated as heat when the rubber is deformed (the smaller the energy loss).
When the low loss rubber with a small loss factor tanδ value is used as the rubber which forms the lower cover rubber layer, it is possible to reduce the rubber deformation when the running conveyor belt travels over the support rollers and to reduce the running resistance. Therefore, the energy loss when the conveyor belt is running is reduced, which contributes to power saving in the motor for driving the belt.
As illustrated in FIG. 6, in a case of a conveyor belt 11 with steel cords 3 as a core, a core layer 2 which is disposed between the upper cover rubber layer 5 and the lower cover rubber layer 6 is configured by covering and embedding a large number of the steel cords 3 arranged in parallel in the belt width direction by a cushioning rubber 4. Ear rubbers 7 are disposed at both ends in the belt width direction. The cushioning rubber 4 is an adhesive rubber used in order to favorably adhere the steel cords 3 to the upper cover rubber layer 5 and the lower cover rubber layer 6 and a thickness t of the cushioning rubber 4, that is, the maximum thickness, is thicker than the nominal diameter of the steel cords 3.
When the rubber deformation when the conveyor belt travels over the support rollers was analyzed in detail, it was found that the cushioning rubber was also deformed in addition to the rubber of the lower cover rubber layer and this deformation was one cause of running resistance. However, there are strict constraints on the blend for the cushioning rubber since it is necessary to prioritize the adhesion between the steel cords and the upper cover rubber layer and the lower cover rubber layer. Therefore, it is difficult to set the blend of the cushioning rubber such that the loss factor tanδ is simply reduced, which is an obstacle to reducing the running resistance when traveling over the support rollers.